1. Field of the Invention
The present invention relates to a fabrication aiding apparatus configured to aid the fabrication of a dental prosthesis such as an inlay, crown, bridge or a like.
2. Description of the Related Art
A conventionally known method for fabricating a dental prosthesis such as an inlay, crown, bridge, or a like includes a method of casting a metal material using a so-called lost wax casting method, a method of forming a ceramic material on a refractory cast and then baking the formed ceramic material using a vacuum electric furnace to fabricate a prosthesis, or a like.
However, to fabricate a dental prosthesis by using the lost wax casing method or the baking method as described, many procedures to be performed manually by a dental technician are required. These procedures present a problem in that they are exact and complicated work, as a result, requiring a lot of process and time. Also, quality of a dental prosthesis varies depending on a degree of skill of a dental technician.
To solve these problems, in recent years, a dental CAD/CAM (Computer Aided Design and Computer Aided Manufacturing) system has been developed in which three-dimensional shape data on a dental prosthesis is created and, based on the three-dimensional data, a dental prosthesis is fabricated by using a machine such as a milling machine, which makes it possible to fabricate a stable-quality dental prosthesis.
In the CAD/CAM system, it is important how determine a margin line between an abutment tooth and a dental prosthesis.
When a margin line is set, as a preparatory step, a plaster model containing an abutment tooth to which a dental prosthesis is applied is fabricated. Next, a plaster model is fabricated with its margin portion made clear, to be used for three-dimensional shape measurement model. That is, in many cases, a margin portion exists within a gingiva and, therefore, by deleting a dispensable portion corresponding to the gingiva from the plaster model, a model having a clear margin portion to be used for the three-dimensional shape measurement is made. Then, by obtaining three-dimensional shape data from the plaster model, and margin line is detected from the obtained three dimensional shape data. As methods for setting a margin line, a method of applying a maximum contour portion as a margin or a method of using a maximum point of infection on an external contour line as a margin line [see, for example, Patent Reference 1 (Japanese Patent Application Laid-open No. 1993-269146)], or a method of using a shadow produced by illuminating a tooth as a margin line [see, for example, Patent Reference 2 (Japanese Patent Application Laid-open No. 2000-185060)] are known.
In the CAD/CAM system, by using a margin line set as above, coping design of a dental prosthesis to be applied to an abutment tooth is done. For example, design of a coping is done so as to obtain three-dimensional coordinates of each of an inner face, outer face, and side face to connect the inner face with the outer face of the coping. The side face of the coping is designated so as to expand from a margin portion in a manner to form a specified angle for example, 40°) with a reference aids being an approximately central axis of a model of an abutment tooth.
However, if the side face of the coping is designated so as to expand in a manner to form a specified angle with the reference axis being an approximately central axis of the model of the abutment tooth as described above, data for fabrication is created in which an angle formed between the inner face of the coping and its side face becomes an extremely acute angle or an obtuse angle, depending on the abutment tooth to be processed. For example, if working by a milling apparatus is performed using the data for fabrication in which the angle formed between the inner face of the coping and its side face has become an extremely acute angle, there is a fear that vibration occurred by milling causes chipping of the coping being fabricated. Moreover, if a coping is to be fabricated using data for fabrication in which an angle formed between the inner face of the coping and its side face is made to be an obtuse angle, a problem arises that, when a position of the coping is adjusted by a dental technician to apply the coping to an abutment tooth, an amount of trimming a side portion of the coping is increased, which requires a lot of work and time.